A process for operation of a data link is for example known from WLAN (Wireless Local Area Network) systems. In this previously known process, a data link between a base station and one or several mobile stations is operated in that data packets are transmitted between the base station and the mobile stations within transmission phases. In WLAN systems, the transmission phases can be constituted by “contention-free” periods. The start of each transmission phase is indicated each time by the emission of a start signal, which clearly can also be described as a beacon signal; after the emission of the beacon signal, the air interface between the base station and the mobile stations for the transmission phase in question is reserved or managed by the base station. Within each transmission phase, the mobile stations are addressed by the base station and called up for the exchange of data packets. Each time after the completion of each transmission phase, there follows a trans-mission pause, in which no transmission of data packets controlled or managed by the base station takes place between the base station and the mobile stations. Since in these transmission pauses the air interface is not managed by the base station, any other devices can gain access to the air interface in these transmission pauses. Accordingly, in WLAN links, these transmission pauses are also described as “contention” periods. In WLAN networks, the sending of the beacon signals by the base station takes place at regular time intervals, for example every 10.24 msecs, so that a new transmission phase is created every 10.24 msecs.
In the previously known WLAN process, the data packets are formed with data of a data stream, in particular a speech and/or video data stream; a received data stream is then created with the received data packets. The access to the transmission medium (air interface) in the previously known WLAN process is normally effected by the CSMA/CA process (carrier sense multiple access with collision avoidance), wherein the individual mobile stations competitively access the air interface. Hence it cannot be predicted when a data packet due for transmission can actually be transmitted.
The standard IEEE802.11e (QoS extensions for WLAN) now offers the possibility of coordinating the access to the medium via the base station (access point). For this, IEEE802.11e defines a functionality “Hybrid Coordination function (HCF)”, which in turn defines a coordination function for the access of the mobile stations to the transmission medium called “HCF Controlled Channel Access (HCCA)”. Put simply, in the process the individual mobile stations which have applied for such a transmission mode are successively interrogated by the base station (Access Point) directly after the beacon emission and their data packets are thus collected. The time conditions for this interrogation mechanism are defined such that a mobile station cannot of itself gain control over the transmission medium.
The U.S. patent application No. 2004/0066783 A1 discloses a process for the organisation of a network with a central structure. In order to manage links with devices which operate with different transmission processes and require different transmission quality levels, for each linkage scheme an identification signal for the link type in question is also supplied. A linkage specification is assigned to each linkage type.
Compared to synchronous transmission processes (compare for example the known DECT (Digital European Cordless Telephone) process), wherein the transmission of a speech data packet always takes place at exactly the same time point relative to the frame start, with the process described at the outset and on which this invention is based the exact time of the transmission within the transmission phase is not fixed. Changes in the transmission times can for example arise through the arrival of further mobile stations or the departure of mobile stations and in some cases through repetitions of unsuccessful transmission attempts; the changes in the transmission times can sometimes considerably influence the transfer rate in the transfer of a data stream, as was found by the inventors.
A process for bandwidth assignment in IEEE802.11e WLAN networks, using a function known as a hybrid coordination function (HCF) and a hybrid coordinator (HC) for access management is known from the publication, L. A. Grieco et al., “A Control Theoretic Approach for Supporting Quality of Service in the IEEE802.11e WLANs with HCF”, Proceedings of the 42nd IEEE Conference on Decision and Control, December 2003. This publication investigates, in particular, how transmission opportunities have to be correctly distributed within a “contention-free” period, while allowing for the time requirements of traffic categories, for example for audio and video applications. The aforementioned publication discloses how an accumulation of signals in a mobile station can be processed for a number of traffic categories in the presence of interference, by allocating the bandwidth of the WLAN network in such a way that the signal accumulation of each traffic category is processed within a contention-free period.